StumbleUpon is hot or what?

Digg and Del.icio.us are great tools to discover interesting content on the web which has been curated by the crowd. Since then, we have had newer tools like Clipmarks and eClips emerge, and have become useful part of our digital lives. Maybe it is time to add StumbleUpon, a web discovery extension for the Mozilla Firefox browser, to the list of these web-curators. For past three weeks, I have been seeing a steady increase in the number of referrers being sent to this site by Stumble Upon. I am sure others are experiencing similar kind of “traffic” referrals.

StumbleUpon uses / ratings to form collaborative opinions on website quality. When you stumble, you will only see pages which friends and like-minded stumblers () have liked. Unlike search engines or static directories, this allows for a true “democracy of the web” – all SU members have a say ( or ) as to whether a page should be passed on. Rating pages as or also improves your stumbles. These ratings connect you to more like-minded members who then show you better pages.

I decided to install it, and well, like Pete Cashmore, I find StumbleUpon simply addictive.

The only answer I can muster is that it’s just so darned addictive – once you Stumble, you just can’t stop. What’s more, it’s incredibly accessible to the mainstream demographic – while mining the social bookmarking sites for gems takes a lot of work, Stumbling takes no effort whatsoever.

StumbleUpon is a Canadian start-up that recently re-located to San Francisco. Matt Marshall reports that they have raised a $1 million from a band of angels including Ron Conway, Mitch Kapor, Rajeev Motwani and Ram Shriram. It was started by Garrett Camp, Geoff Smith, and Justin LaFrance, who bootstrapped the company for much of its early life.

The company has been around for nearly four years, but has now been hitting its stride. Apparently, nearly 850,000 people are using the tool, and have reviewed, rated, and categorized over five million web pages since the service was first launched. Will it continue on this growth curve and become as valuable? What do you think?